1. Technical Field
This invention relates generally to loudspeakers. More particularly, this invention relates to loudspeakers having a compression driver with a horn, where the compression driver has a phasing plug.
2. Related Art
Loudspeakers transform electrical signals into sound. Many loudspeakers have a compression driver with a horn. The compression driver usually is a transducer having a diaphragm with a voice coil immersed in the magnetic field of a permanent magnet. The diaphragm vibrates when electrical signals are applied to the voice coil. The vibrations of the diaphragm compress air to produce sound from the loudspeaker. The diaphragm may be flat, concave, convex, or a combination. The diaphragm may comprise paper, cloth, plastic, metal, ceramic, or a combination of materials. The horn is a tube with increasing cross-section across its axis, thus forming a flared, conic configuration. The horn's narrow inlet or throat is connected to the compression driver. The horn's wide outlet is for projecting sound. The horn generally acts as a waveguide to direct the pattern of sound waves from the compression driver. These horn-loaded compression drivers may be designed specifically to provide low, high, or midrange sound frequencies.
Many horn-loaded compression drivers have a phasing plug between the diaphragm and the horn. The phasing plug is positioned adjacent to the diaphragm with sufficient space so the phasing plug does not interfere with the diaphragm as it vibrates. The phasing plug has a surface facing the diaphragm that generally conforms or lays parallel to the surface of the diaphragm. The phasing plug also has an opposing surface facing the throat of the horn. The phasing plug typically has circumferential slits, radial slits, or holes that form an acoustic path for transfer of the sound energy from the compression driver to the horn. This acoustic path should compresses audio signals from the compression driver and equalizes path lengths of the sound waves to reduce out of phase and destructive interference.
Horn-loaded compression drivers have several performance advantages including increased sensitivity, desirable pattern control, arrayability (easier driver arrangement in a speaker enclosure), reduced harmonic and intermodulation distortion, and higher maximum sound pressure level (SPL). However, these advantages often are difficult to achieve due to limitations in the practical implementation of an effective phasing plug, especially in loudspeakers designed for midrange sound frequencies. Phasing plugs usually do not provide a satisfactory and/or complete transformation of the acoustic signals from the compression driver to the horn. These limitations result in poor frequency response characteristics, restricted bandwidth in the upper frequency range, and non-ideal area expansions that introduce audible response irregularities such as the “horn midrange sound” in midrange loudspeakers having horn-loaded compression drivers.